Applications of high-potential quinones. Part V. Ring B oxidation in the podocarpic acid series

Abstract

Phenols of the podocarpic acid series undergo exclusive oxidation in ring B at room temperature with 2,3-dichloro-5,6-dicyanobenzoquinone in alcoholic solvents. Two equivalents of the quinone yield mainly the corresponding 7-ketones by attack at the benzylic methylene groups, while the use of three equivalents provides a convenient one-step synthesis of the 5,6-dehydro-7-ketones. Dehydrogenation in non-oxygenating solvents did not consistently give the corresponding styrenes, although these were obtained, in some cases, via reduction of the 7-ketones.